The invention relates to a pressure-contact and lift-off arrangment for working elements which are sequentially arranged in a processing unit for exposed printing materials, wherein the print materials are guided, in continuous succession, across the surface of a table, where they are developed and cleaned.
In processing units for printing plates, papers or films with photosensitive coatings, or similar materials which are developed after exposure to produce an image, transport devices and squeezing-off devices are provided. These devices generally comprise two rollers which can be pressed against one another, and which simultaneously effect the forward transportation of the printing plates. The rollers also squeeze off excess liquid developer, or any other chemicals which may be used in the developing process, as well as squeeze off the cleaning fluid from both sides of the printing material. Viewed in the direction in which the printing materials are transported through the processing unit, doctor-blade devices are frequently installed in advance of and/or following the transport and squeezing-off devices. These doctor blades wipe off any residual amounts of liquid which may still be present in advance of and following the individual processing stations. In this manner, the doctor blades prevent each liquid in question from being dragged into a processing station located downline.
The rotating and oscillating brushes which are installed within the developing station assist the developing process to which the printing plate is being subjected, in conjunction with the simultaneous action of a cleaning fluid.
In practice, each of these working elements is mounted individually (German Offenlegungsschrift No. 2,336,122), and is also individually pressed against the printing materials which runs across the surface of the table. No arrangements are provided for the simultaneous, slight lifting of all the working elements from the contact surface, or for the simultaneous lifting of all the elements clear of the surface. Means are only provided for lifting the working elements individually, either slightly from the surface or clear of it.
In the case of the foregoing arrangement, since a separate control handle is assigned to each end of each upper roller, in order to lift off the upper rollers, as is necessary before comparatively long shutdown periods, for example overnight, or during a weekend, disadvantageously, a large number of control handles must be operated. The operation of these handles is convenient and time-consuming, so that operators are occasionally tempted to neglect these control actions. If, however, the rollers remain pressed against one another over comparatively long shutdown times, deformation of their surfaces can occur. Such deformation can endanger the reliability and gentleness of the transportation of the printing plates, as well as endanger the degree of perfection of the process whereby the liquids are squeezed-off, above all in the case of horizontal processing systems.
The state of the art likewise includes an arrangement for developing printing plates in which rollers are installed in pairs with their ends mounted in side plates. These side plates are divided such that their complete upper portion or, as the case may be, the complete upper portion of the processing zone including all the upper rollers, can be lifted slightly by means of a pivot point which is assigned to the upper side plate. The side plates are equipped with appropriate lifting elements in order to permit this function to be performed.
This arrangement is comparatively expensive and obliges the operator to exert considerable force. This arrangement cannot be used for facilities of the type which have a plurality of treatment stations, and in which each treatment station is designed as a constructional unit which can be assembled with further constructional units to form the complete facility.
U.S. Pat. No. 3,846,816 discloses a processing facility for printing plates which possesses a stationary lower portion and an upper portion which can be tilted relative to the lower portion about a horizontal axis. An electrically-operated screw type lifting device is fastened to the upper portion to lift or lower it as required. The lifting device is connected to switching devices which react to pressure and which are attached to both portions of the processing appliance. Rollers are mounted in the upper portion, these rollers being raised with this upper portion when it is tilted away. In the case of this appliance, it is disadvantageous that the various liquids can drip from the rollers into the adjacent processing stations, since the upper portion does not remain parallel on being lifted slightly from the lower portion. The upper portion is only hinged, and thus moves upward at an angle. Moreover, opening the processing appliance results in more rapid evaporation of the developer.
U.S. Pat. No. 4,206,527 discloses a printing plate developing facility having upper and lower rollers for transporting the printing plates. These rollers are arranged horizontally in pairs and squeeze off any residual liquid adhering to the printing plates. At each end, each upper pressure roller possesses a bearing which is installed in a manner such that it can be raised and lowered in relation to the lower roller, and which is moved by means of a toggle-lever arrangement. The bearings of the upper rollers are moved, in each case, by means of a pivotable fork head having an upper arm and a lower arm. The pivot axis of the fork head is aligned in a manner such that it is parallel to the direction in which the printing plates are transported. When the bearing is in the lowered state, the toggle-lever arrangement presses the upper arm downward, onto the bearing, while in the raised state the bearing is supported by the lower arm. A first end of each toggle-lever arrangement is connected to the fork head, and a second end of each toggle-lever arrangement is connected to a rotatable control shaft which is common to all the toggle-lever arrangements, and which is mounted parallel to the direction in which the printing plates are transported.
When the pressure rollers are unloaded, but have not been lifted clear, dried-on cleaning fluid and/or gumming residues generally lead to patches of adhesion in the region of the roller gap. Adhesions of this nature can cause damage to the surfaces of the rollers, and of the printing material. It is also disadvantageous that the doctor-blade device can become glued to the surface against which it bears as a result of the drying-on of decoating fluid. This can lead to damage of the lip of the doctor blade in the process of removing the doctor-blade device, or when the next printing plates run through the unit. If the processing unit contains oscillating brushes and/or rotating brushes as working elements, a problem occurs if the bristles of the brushes are not raised when the unit is shut down overnight, or during the weekend, and remain under load. In this situation, the bristles, which are pressed against the contact surface, cannot spring back again into their unloaded starting position. This results in a shortening of the useful life of the bristles as compared to the case where the brushes are raised. Moreover, the deformation experienced by the bristles adversely affects the operational reliability of the brushes.